This invention relates to an improved frame for a seat backrest and to a seat backrest and/or seat incorporating this frame.
The invention has particular application to seats for automobiles. For ease of description, the invention is illustrated with reference to that application. However, it is to be understood that the seat backrest frame of the invention can be used in seats other than automotive seats.
In known forms, the frame for a vehicle seat backrest usually is made from components of steel tubing or pressed steel plate. The components are shaped and assembled to provide a somewhat rectangular peripheral frame, with this usually being strengthened by at least one transverse member which is secured to and extends between respective side portions of the peripheral frame. Usually, a transverse member is provided between the side portions at what is to be an upper region of the frame in a normal in-use orientation. Also, a longitudinally adjustable band of resilient material, such as a suitable plastics material, often is provided between the side portions, at a lower region of the frame, to enable lumbar region adjustment of a seat backrest in which the frame is to provide structural form.
With known forms of frame, padding, such as foam plastics, horsehair, jute fibre (often rubberised) and polyester or other synthetic fibre, is provided over the frame and any transverse member. An outer cover, such as a fabric or leather cover, then is fitted over the frame and foam padding to provide a finished seat back. The padding of course is provided to impart a suitable contour form to the seat backrest for the comfort and support of a user, while the outer cover is to assist in retaining the padding in relation to the frame and to provide a suitable finish. The form and thickness of the padding also is to be such as to protect a user against injury from the relatively rigid frame in the event of a vehicle impact.
To accommodate typical impact loadings, the steel components used to form the frame needs to be of a gauge providing sufficient strength to withstand at least usual loading levels, as specified in legislation or regulations in various countries. As a consequence, the weight of the frame is substantial, despite vehicle manufacturers being concerned with reducing weight in all components to the extent that this is consistent with safety requirements.
In addition to the substantial weight of the steel frame, it is to be appreciated that the weight of padding is substantial. Thus, while the padding has a low density relative to the frame per se, the volume of foam or other material necessary to form the padding, and hence the weight of padding, is substantial. In a typical vehicle seat back, the foam padding contributes approximately 25% of the weight. Also, padding is expensive, particularly as defects in its production is a major cause of rejects. Moreover, the padding usually is shaped so as to provide wing portions of a vehicle seat back, to function as lateral restraints for a user, although the padding has relatively low resistance to deformation and gives way in side impacts, and then is unable to provide such restraint. The resistance of the padding can be increased by metal wire or metal plate reinforcement but this also can deflect under side impacts.
There accordingly is a number of deficiencies in the known forms of vehicle seat backrest frames, and in backrests including these frames. The present invention is directed to overcoming at least some of these deficiencies by providing an improved seat backrest frame and a backrest and/or seat including the improved frame.
A seat backrest frame according to the present invention is in the form of a rigid peripheral frame structure which, relative to an in-use orientation, has frame portions including laterally spaced, upstanding side portions, an upper transverse portion which joins the upper ends of the side portions and a lower transverse portion which joins the lower end of the side portions. The frame structure also may include a further transverse portion which joins the side portions at an intermediate level, preferably a minor part of the length of the side portions below the upper transverse portion.
The frame structure is integrally formed by casting from a suitable light alloy or by moulding from a suitable engineering plastics material. Each frame portion is of elongate channel form, defined by respective side flanges and an interconnecting web, with the web disposed forwardly of the frame structure and the channel of each frame member opening rearwardly. The rear edge of the side flanges of each frame portion may be on or closely adjacent to a common plane, while the transverse members may be of substantially uniform section throughout a major portion of their length. However, each side portion, over at least the lower half of its length, defines a respective forwardly projecting wing (or bulge) in which the depth of its channel is substantially greater than the depth of the channel of each transverse portion.
The wing of each side portion is such as to provide a number of significant benefits. The first is that each wing results in the frame providing for lateral restraint of an occupant for a seat having the back rest frame. Thus, while it is desirable that a layer of padding be provided over the frame, including each wing, the overall volume of padding is able to be substantially less than is required with known forms of backrest frames. This is particularly the case where, in the known frames, the padding itself is to define a wing portion for such restraint.
A further practical benefit is that a chamber defined in each wing, as a result of enlargement of the channel of each side portion, can be used to house ancillary devices. Thus, one or each wing can accommodate an airbag or cushion device which is inflatable forwardly through a suitably positioned opening of the side portion for the benefit of the seat occupant, in the event of a collision. Alternatively, the wing can accommodate such airbag, or a further airbag, which is rearwardly inflatable for the benefit of a rear seat occupant. Additionally, or alternatively, each wing can accommodate therein a part of the anchoring and/or adjustment mechanism for a lumbar support device to be incorporated in a seat-back having the frame. Additionally, or alternatively the wing can accommodate at least one motor drive for various power operated systems in the seat, such as a lumbar adjuster or a power recline adjuster.
The side portions may be substantially parallel. The upper and lower portions may extend generally at right angles to the side portions. However, the upper portion, or each of the upper and lower portions, may have end sections which are inclined slightly relative to a mid-section thereof, such that the generally rectangular form of the frame has inclined upper, or upper and lower shoulders by which the lower and upper portions merge with each side portion.
As indicated, the frame may include at least one further transverse member which extends between and is connected to, or integral with, each side portion. Preferably such further transverse member is spaced from the upper portion by a minor part of the length of the side portions, so as to be located in an upper part of the frame when the latter is in an in-use orientation.
The frame portions are such that the frame is in the form of a hollow shell structure which is open at the rear thereof along substantially the full length of each frame portion. That is, each frame portion may comprise only its side and front walls, so as to be of channel form. The arrangement can be such that, in the in-use orientation of the frame, a continuous rearwardly open channel is defined around the frame.
The or each further transverse member may be of similar cross-section to the frame portions. Thus, a transverse member can be of channel form, such as with a rearwardly open channel.
The frame may be formed integrally with any further transverse member, and this preferably is the case. Where the frame is cast, it most preferably is produced from a suitable light alloy comprising a magnesium, aluminium or zinc alloy, such as by pressure die casting. The use of a magnesium alloy is preferred. Where the frame is moulded, it may be produced from a suitable high strength engineering plastics material, such as by injection or compression moulding. The frame also can be compression moulded from a composite material such as synthetic mineral, or ceramic fibre reinforced plastics material. Alternatively, the frame may be moulded from fibre-reinforced plastics material, by use of conventional procedures, such as by laying-up fibrous material in a mould, applying a suitable plastics material to the fibrous material, and then curing the plastics material.
The frame of the invention has the benefit of enabling it to be of thin-walled construction, with walls as thin as from 2 to 3 mm, or even less. The actual thickness can vary with the structural material used, and the method appropriate for production of the frame from that material. Also, depending on requirements, the wall thickness can vary in different parts of the frame, as detailed later herein.
The frame according to the invention may, and preferably does, have a cross-section which is greater than that typical of the known tubular steel frames. In one form of the invention, the frame is such that it contributes substantially to the overall profile form or configuration of a seat backrest of which it forms a part. Thus, the frame may be such that it provides part of the function of padding in the known form of seat backrests, in that the padding can be used principally only to provide for passenger comfort rather than also to define the profile or configuration of the seat backrest.
In the known form of the steel frame for a vehicle seat backrest, in which components are of tubular steel, the latter is of a minimum diameter and wall thickness consistent with achieving a required balance between weight and rigidity. Similar considerations apply where the components are of pressed steel plate. In each case, the steel frame contributes to the overall somewhat rectangular form of the seat backrest, but not to other factors of the backrest profile or configuration. That is, the known steel frame does not as a practical matter, provide the depth, profile or configuration of the seat, while it usually does not provide for substantial lateral constraint. Rather, these factors are provided by the padding and any wire or plate reinforcement in the padding and, as indicated, this necessitates the use of a substantial volume, and hence weight, of padding.
Whereas the tubular or pressed steel components of the known forms of frame may have an outside diameter of about 20 mm to 30 mm, the frame portions of the frame of the invention most preferably have cross-sectional dimensions substantially in excess of such diameter. While those dimensions can vary from one frame portion to another, and even in a given frame portion, the dimensions may be a minimum of 35 mm or more in both the spacing between the inner and outer side walls (ie. in the width of the channel) and also in the depth of those walls (ie. in the depth of the channel). Moreover, in each side portion of the frame, at least at a lower extent of each at which a wing is defined, the depth of its side walls and/or the spacing therebetween can be substantially greater than such dimensions. In such lower extent, the dimensions may be up to about 160 mm for the depth of the side walls, and up to about 90 mm for the spacing between them.
As will be appreciated, the frame of the invention can be such as to define a peripherally continuous channel, or a respective channel in each of its frame portions, which is of substantial volume. Relative to the known form of frames, this represents a volume in which the provision of padding is not required. Also, in the case of part of the volume defined in a lateral restraint lower portion of the side portions, the frame as indicated enables accommodation of power motor devices and/or of anchoring and adjustment means for an adjustable lumbar support for a seat backrest and, if required, accommodation for an inflatable safety air-bag for lateral protection of a user in the event of a collision.